#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <string>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>

using namespace std;

const int basesize = 1024;
const int argvnum = 64;
const int envnum = 64;
// 全局的命令行参数表
char *gargv[argvnum];
int gargc = 0;

// 全局的变量
int lastcode = 0;

// 我的系统的环境变量
char *genv[envnum];

// 全局的当前shell工作路径 
char pwd[basesize];
char pwdenv[basesize];

// 全局变量与重定向有关
#define NoneRedir   0
#define InputRedir  1
#define OutputRedir 2
#define AppRedir    3

int redir = NoneRedir;
char *filename = nullptr;

// "    "file.txt
#define TrimSpace(pos) do{\
    while(isspace(*pos)){\
        pos++;\
    }\
}while(0)

string GetUserName()
{
  string name = getenv("USER");
  return name.empty() ? "None" : name; 
} 

string GetHostHome()
{
  string hostname = getenv("HOSTNAME");
  return hostname.empty() ? "None" : hostname;
}
  
string GetPwd()
{
  if(nullptr == getcwd(pwd,sizeof(pwd)))
   return "None";
  snprintf(pwdenv,sizeof(pwdenv),"PWD=%s",pwd);
  putenv(pwdenv);
  return pwd;
}

string LastDir()
{
  string curr = GetPwd();
  if(curr == "/" || curr == "None") return curr;
  size_t pos = curr.rfind("/");
  if(pos == std::string::npos) return curr;
  return curr.substr(pos+1);
}

string MakeCommandLine()
{
  char command_line [basesize];
  snprintf(command_line,basesize,"[%s@%s %s]# ",GetUserName().c_str(),GetHostHome().c_str(),LastDir().c_str());
  return command_line;
}

void PrintCommandLine()
{
  printf("%s",MakeCommandLine().c_str());
  fflush(stdout);
}

bool GetCommandLine(char command_buffer[],int size)//获取用户命令
{
  char * result = fgets(command_buffer,size,stdin);
  if(!result)
  {
    return false;
  }
  command_buffer[strlen(command_buffer)-1] = 0;
  if(strlen(command_buffer) == 0) return false;
  return true;

}

void ParseCommandLine(char command_buffer[],int len)//分析命令,将命令拆开
{
 (void) len;
 memset(gargv,0,sizeof(gargv));
 gargc = 0;
 const char *sep = " ";
 gargv[gargc++] = strtok(command_buffer,sep);
 while((bool)(gargv[gargc++] = strtok(nullptr,sep)));
 gargc--;
}
void debug()
{
    printf("argc: %d\n", gargc);           // 打印参数个数
    for(int i = 0; gargv[i]; i++)          // 遍历所有参数
    {
        printf("argv[%d]: %s\n", i, gargv[i]);  // 打印每个参数
    }
}

bool ExecuteCommand()
{
  pid_t id = fork();
  if(id<0) return false;
  if(id == 0 )
  {
    execvpe(gargv[0],gargv,genv);
    exit(1);

  }
  int status = 0;
  pid_t rid = waitpid(id,&status,0);
  if(rid>0)
  {
    if(WIFEXITED(status))
    {
      lastcode = WEXITSTATUS(status);

    }
     else
        {
            lastcode = 100;
        }
        return true;
    }
    return false;
}

void AddEnv(const char *item)
{
    int index = 0;
    while(genv[index])
    {
        index++;
    }

    genv[index] = (char*)malloc(strlen(item)+1);
    strncpy(genv[index], item, strlen(item)+1);
    genv[++index] = nullptr;
}

bool CheckAndExecBuiltCommand()
{
    if(strcmp(gargv[0], "cd") == 0)
    {
        // 内建命令
        if(gargc == 2)
        {
            chdir(gargv[1]);
            lastcode = 0;
        }
        else
        {
            lastcode = 1;
        }
        return true;
    }
    else if(strcmp(gargv[0], "export") == 0)
    {
        // export也是内建命令
        if(gargc == 2)
        {
            AddEnv(gargv[1]);
            lastcode = 0;
        }
        else
        {
            lastcode = 2;
        }
        return true;
    }
    else if(strcmp(gargv[0], "env") == 0)
    {
        for(int i = 0; genv[i]; i++)
        {
            printf("%s\n", genv[i]);
        }
        lastcode = 0;
        return true;
    }
    else if(strcmp(gargv[0], "echo") == 0)
    {
        if(gargc == 2)
        {
            // echo $?
            // echo $PATH
            // echo hello
            if(gargv[1][0] == '$')
            {
                if(gargv[1][1] == '?')
                {
                    printf("%d\n", lastcode);
                    lastcode = 0;
                }
            }
            else
            {
                printf("%s\n", gargv[1]);
                lastcode = 0;
            }
        }
        else
        {
            lastcode = 3;
        }
        return true;
    }
    return false;
}

void InitEnv()
{
    extern char **environ;
    int index = 0;
    while(environ[index])
    {
        genv[index] = (char*)malloc(strlen(environ[index])+1);
        strncpy(genv[index], environ[index], strlen(environ[index])+1);
        index++;
    }
    genv[index] = nullptr;
}
void ParseRedir(char command_buffer[], int len)
{
    int end = len - 1;//假如长度为18，那最后一个字符下标为17
    while(end >= 0)//从后往前找
    {
        if(command_buffer[end] == '<')
        {
            // 输入重定向处理
            redir = InputRedir;
            command_buffer[end] = 0;        // 截断命令字符串，令他置为0后，C语言的字符串函数（如execvp）遇到 \0 就认为字符串结束，也就是将命令和文件名分开
            filename = &command_buffer[end] + 1;  // 获取文件名
            TrimSpace(filename);            // 去除文件名前后空格
            break;
        }
        else if(command_buffer[end] == '>')
        {
            if(command_buffer[end-1] == '>')
            {
                // 追加重定向处理 ">>"
                redir = AppRedir;
                command_buffer[end] = 0;
                command_buffer[end-1] = 0;  // 两个字符都要置零
                filename = &command_buffer[end]+1;
                TrimSpace(filename);
                break;
            }
            else
            {
                // 输出重定向处理 ">"
                redir = OutputRedir;
                command_buffer[end] = 0;
                filename = &command_buffer[end]+1;
                TrimSpace(filename);
                break;
            }
        }
        else
        {
            end--;
        }
    }
}
void DoRedir()
{
    if(redir == InputRedir)
    {
        if(filename)
        {
            int fd = open(filename, O_RDONLY);  // 只读打开文件
            if(fd < 0) { exit(2); }            // 打开失败
            dup2(fd, 0);                       // 标准输入重定向
        }
        else { exit(1); }                      // 无文件名
    }
    else if(redir == OutputRedir)
    {
        if(filename)
        {
            // 创建文件，如果存在则清空
            int fd = open(filename, O_CREAT | O_WRONLY | O_TRUNC, 0666);//666在O|CREAT中用到，赋予读写权限
            if(fd < 0) { exit(4); }
            dup2(fd, 1);                       // 标准输出重定向
        }
        else { exit(3); }
    }
    else if(redir == AppRedir)
    {
        if(filename)
        {
            // 创建文件，如果存在则追加
            int fd = open(filename, O_CREAT | O_WRONLY | O_APPEND, 0666);
            if(fd < 0) { exit(6); }
            dup2(fd, 1);                       // 标准输出重定向
        }
        else { exit(5); }
    }
    // 没有重定向则什么都不做
}
int main()
{
  while(true)
  {

  char command_buffer[basesize];
        PrintCommandLine(); // 1. 命令行提示符
        // command_buffer -> output
         if( !GetCommandLine(command_buffer, basesize) )   // 2. 获取用户命令
        {
            continue;
        }
        printf("%s\n", command_buffer);

         //printf("%s\n", command_buffer);
        //ls
        //"ls -a -b -c -d"->"ls" "-a" "-b" "-c" "-d"
        ParseCommandLine(command_buffer, strlen(command_buffer)); // 3. 分析命令

        if ( CheckAndExecBuiltCommand() )
        {
            continue;
        }

        ExecuteCommand();   // 4. 执行命令
  }
    return 0;
}
